Current methods for detecting and quantifying nucleic acids in multiplexed assays are limited, especially those assays that utilize fluorescent dyes for detection. For example, White discusses the problems of multiplexing using the TaqMAN® assay (Trends in Biotechnology (1996) 14(12); 478-483). Among other issues, fluorescent dyes offer only limited multiplexing options, and currently available methods that attempt to overcome these limitations, for example, by using primer-extension and ligation-based SNP analysis followed by universal PCR and hybridization to chip arrays are often very time consuming (e.g., 1-2 days).
The use of mass spectrometry offers a solution for improved multiplexing because of the increased number of detection channels, but the practical utility of previously disclosed mass spectrometry-based methods can be further improved. For example, the use of high-specificity hybridization of peptide nucleic acid (PNA) probes to PCR-amplified DNA and subsequent detection by mass spectrometry is described by Ross (Anal. Chem (1997) 69:4197). Also, a primer extension method and detection of the primer extension product by mass spectrometry is described by Haff (Nucleic Acids Res. (1997) 25:3749). Additional mass spectrometry-based methods are described by Jurinke et al (Adv Biochem Eng Biotechnol (2002) 77:57-74).